1. Field of the Invention
The present invention relates to a backlight unit and in particular to a backlight unit using optical fibers.
2. Discussion of the Related Art
Flat panel display device are typically very thin and light, making them particularly well suited for application as the display for portable data devices such as notebook computers, mobile phones, and PDAs. The liquid crystal display (LCD) device, which is one type of flat panel display device, controls light transmittance of a liquid crystal layer having dielectric anisotropy by applying and controlling an electric field to thereby displaying an image. To this end, the liquid crystal display device includes a liquid crystal display panel having liquid crystal cells arranged in a matrix and the light transmittance is controlled for a liquid crystal cell for each pixel. A backlight unit emits white light onto the liquid crystal display panel to allow the image to be viewed.
For portable applications employing flat panel display devices, it is important that electric power consumption be reduced to a minimum. With the exception of reflective flat panel display devices using ambient light for displaying images, flat panel displays typically employ a backlight unit. The primary determinant of power consumption for flat panel display devices is the electric consumption power is the backlight unit. For example, for a notebook computer hundreds of candela are used to suitably display images on a liquid crystal display device. A light source having high luminescence and capable of delivering uniform brightness over the display area is used to supply the light for a flat panel display device. To this end, a number of backlight systems have been proposed.
Among the proposed systems is a backlight system using optical fibers to transmit light over long distances without loss, and using low electric power consuming light emitting diodes (LEDs) as the light source. The light from the LED can transmitted over a distance and distributed over a relatively large area using the optical fibers. Further, a backlight unit using optical fiber is freely and easily flexed. Therefore, backlight systems employing optical fibers can be used not only with LCD devices using hard substrates but also with flexible LCD devices using soft plastic substrates.
FIG. 1 is a diagram illustrating a flexible backlight unit of the related art, and FIG. 2 is a diagram showing optical fibers of a light emitting plate of the flexible backlight unit of the related art in detail.
Referring to FIGS. 1 and 2, the flexible backlight unit of the related art includes: a light emitting plate 10 formed of a plurality of optical fibers 10A weaved to have a plurality of meandering parts alternatively; a diffusion plate 12 disposed on an upper surface of the light emitting plate 10; a reflection plate 14 disposed in a lower part of the light emitting plate 10; a light source 16 connected to one end of the light emitting plate 10 for emitting light into the optical fibers 10A; and a connection terminal 18 to connect the light emitting plate 10 to the light source 16. In addition, the backlight unit of the related art further includes a plurality of optical sheets (not shown) disposed on the upper part of the diffusion plate 12.
As shown in FIG. 2, the light emitting plate 10 is formed by weaving the optical fibers 10A together with threads 10B having a thickness similar to that of the optical fibers 10A. The optical fibers 10A woven together with the threads 10B are evenly spread out over the width of the light emitting plate 10 so that the light emission area is broadened to cover light emitting plate 10. The ends of the optical fibers are bundled at one end at one side of the light emitting plate 10 and connected to the light source 16 by the connection terminal 18.
The connection terminal 18 transmits the light exiting from the light source 16 to the optical fibers 10A bundled together at the connection terminal.
The diffusion plate 12 is disposed on an upper surface of the light emitting plate 10 to diffuse the light which emitted from the light emitting plate 10.
The reflection plate 14 is disposed at the lower part of the light emitting plate 10 to reflect the light emitted downward from the light emitting plate 10 in an upwards direction towards the lower part of the diffusion plate 12.
The light source 16 is connected through the connection terminal 18 to each of the bundled optical fibers 10A to emit light into the optical fibers 10A.
The flexible backlight unit of the related art, as shown in FIG. 2, includes the optical fibers 10A woven with the thread 10B. Accordingly, the optical fibers 10A are formed into a meandering shape (curved pattern) by the thread 10B woven into the flexible backlight unit, as in FIG. 3. When the light from the light source 16 is emitted to the inside of the optical fibers 10A, the total reflection condition within the optical fibers 10A is disturbed within the curved pattern, and the light emitted into the inside of the optical fibers 10A from the light source 16 is made to exit the optical fibers 10A at the curved portions, allowing the optical fibers to emit light onto the flexible liquid crystal display device.
The flexible backlight unit of related art connects the optical fibers 10A and the light source 16 through the connection terminal 18 so that light emitted from the light source 16 is transmitted into the optical fibers 10A. The optical fibers 10A are tied up into a bundle to connect the optical fibers 10A to the light source 16 through the small connection terminal 18. Accordingly, as shown in FIG. 4, a bundle area A is formed at the location where the optical fibers 10A are tied up in the shape of bundle in the light emitting plate 10 of the flexible backlight unit using the optical fiber of the related art. Accordingly, the flexible liquid crystal display device to which the flexible backlight unit using the optical fiber of the related art is applied has a disadvantage in that a bezel area at least as large as the bundle area A of the light emitting plate 10 is occupied.
As illustrated in FIG. 5, the bezel area is at an outer area of the screen of the liquid crystal display device, and the bezel area becomes uselessly bulky if it is needlessly enlarged, since the bezel area is a non display area in the liquid crystal display device.
In order to reduce the bezel area, the bundle area A of the light emitting plate 10 may folded to the side of the flexible backlight unit as shown in FIG. 6A. However, in the flexible backlight unit using the optical fiber of the related art, the bundle area A of the light emitting plate 10 may be longer than the width W of the light emitting plate 10. Accordingly, there remains an area B having a size corresponding to the difference between the width W of the light emitting plate 10 and size of the bundle area A of the light emitting plate 10 even when the bundle area A of the light emitting plate 10 is folded to the side of the flexible backlight unit. Accordingly, there is a limit to the amount of reduction of the bezel area that can be accomplished by folding the bundle area A of the light emitting plate 10 to the side of the backlight unit.
In another method for reducing the bezel area, the bundle area A of the flexible backlight unit is bent towards the rear of the flexible backlight unit, as shown FIG. 6B. However, in this method of bending the bundle area A of the light emitting plate 10 to the rear of the flexible backlight unit, there is a limit to the amount of reduction of the bezel area that can be accomplished by folding the bundle area, because the sharpness of the bend is limited to prevent the optical fiber from becoming broken by being bent more sharply than a critical value. For example, the an optical fiber may be prevented from bending in an arc having less than a permissible minimum bending radius of 1.6 mm.